At present, multi-stage hydraulic fracturing of horizontal well is one of the most effective technical means for developing unconventional low-permeability reservoirs. By densely placing perforation clusters in the fracturing stage, the engineers hope that this technology can form closely distributed and uniform hydraulic fractures within the pay zone to significantly increase the permeability and hydrocarbon productions. However, in recent years, the engineers have realized from the monitoring data that there is often a serious non-uniformity of fracture growth extents in the hydraulic fracturing. During the multi-stage hydraulic fracturing process, most of fracturing fluids only flow into few of hydraulic fractures, hence that most of hydraulic fractures cannot obtain enough fracturing fluids. As a result, a large proportion of hydraulic fractures gradually slows down or even stops their growths with time. The non-uniformity of fracture growth extents damages the performance of fracturing stimulations, at least in two different aspects. First, the hydraulic fractures are not evenly developed, therefore the reservoir is not completely stimulated, which causes a serious waste of construction costs. Second, a small portion of hydraulic fractures acquire too much fracturing fluids and their growth extents are out-of-control. These oversize hydraulic fractures may touch with the neighboring wells to generate a serious inter-well interference, which leads to a reduction of production in neighboring wells. Therefore, whether or not the uniform fracture growth can be maintained is a key factor affecting the performance of multi-stage hydraulic fracturing in horizontal wells. In the past 20 years, a large number of engineers and researchers have studied the physical mechanism for the occurrence of non-uniform fracture growth. These research results show that two factors, namely, the rock physical heterogeneity and stress shadowing, play important roles in the occurrence of non-uniform fracture growth.
In order to maintain the uniform fracture growth in multi-stage hydraulic fracturing of horizontal well, some researchers have proposed several treatments, e.g., the limited-entry method, cluster spacing optimization and fluid diversion, to control the differences between fracture growth extents. Among them, the limited-entry method is relatively simpler in operation and lower in cost, and thus has been widely used in the field. The core theory of this technology is that the perforation friction at fracture inlet can be increased by adjusting the design of the perforation parameters to balance the fluid resistances through each fracture, thereby maintaining the balance of the fluid supply and fracture growth extents. Field practice has shown that the limited-entry method has obvious improvement effects on the uniformity of fracture growth extents, but its performance relies heavily on the reasonable design of the perforation parameters. The effectiveness of limited-entry method with poor design of perforation parameters will be gradually lost during the fracturing process, partly due to the perforation erosion. Mistakes in the design of perforation parameters may even exacerbate the uniformity of fracture growth extents. At present, due to the lack of scientific methods for optimizing the design of perforation parameters, many engineers have implemented design based on their own engineering experiences, resulting in unstable performances of limited-entry method on site. Thus, there exists a need to provide a method for optimizing perforation parameters to maintain uniform fracture growth in multi-stage hydraulic fracturing of horizontal well.
It should be noted that the above description of the technical background is merely for the purpose of facilitating a clear and complete description of technical solutions of the present invention, and is convenient for understanding by those skilled in the art. The above technical solutions should not be considered to be well-known to those skilled in the art, simply because these aspects are set forth in background segment of the present invention.